Charging method for sub-module based hybrid converter

ABSTRACT

A sub-module based hybrid converter is provided. By setting a half-controlled charging link of changing full bridge sub-modules from a blocked state to a half-blocked state one by one in a charging process, and raising the voltages of half bridge sub-modules to reach the starting point of a half bridge sub-module based self-powered supply in an uncontrolled stage of the half bridge sub-modules, the starting point of the sub-module based self-powered supply is increased, and the design difficulty of the sub-module based self- powered supply is reduced. The present invention also includes another charging method for a sub-module based hybrid converter.

RELATED APPLICATIONS

This application is the U.S. National Phase of and claims priority toInternational Patent Application No. PCT/CN2018/072417, InternationalFiling Date Jan. 12, 2018; which claims benefit of Chinese PatentApplication No. 201710029574.5 filed Jan. 16, 2017; both of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the field of High Voltage DirectCurrent (HVDC) transmission and distribution, and in particular, to acharging method for a sub-module based hybrid converter.

BACKGROUND OF THE INVENTION

High Voltage Direct Current (HVDC) transmission uses a voltage sourceconverter, which can independently and rapidly control active power andreactive power, thereby improving system stability, suppressing thefluctuation of system frequency and voltage, and enhancing steady-stateperformance of a grid-connected AC system. The HVDC transmission hasgreat advantages in the fields of renewable energy grid-connection,distributed generation grid-connection, island power supply, and urbandistribution network power supply, etc. As the core device in the HVDCtechnology, a Modular Multilevel Converter (MMC) is the preferredsolution for the current HVDC transmission projects due to itsmodularization, low switching frequency, and good harmonic performance,etc.

The MMC solution-based HVDC transmission projects which have been putinto operation at present adopt a Half Bridge sub-module based ModularMultilevel Converter (HB-MMC) solution. If a short-circuit fault occursto the DC side of the converter, an AC power supply, an antiparalleldiode in the half bridge sub-module, and a short-circuit fault pointform a short-circuit loop. Since the high-voltage DC circuit breakertechnology and manufacturing process are not yet mature at this stage,it is necessary to isolate the fault circuit by disconnecting the ACcircuit breaker, and restarting is made only after the fault currentnaturally decays to 0. This solution is longer in delay for powerrestoration, and thus the reliability of power supply is reduced.

To endow a DC fault clearance capability to the converter, domestic andforeign scholars have proposed many novel topologies. The proposer ofMMC, German scholar R. Marquart proposes a generalized MMC concept withsub-modules as the basic power units and proposes a novel sub-moduletopology such as a Full Bridge Sub-Module (FBSM). However, the FullBridge sub-module based Modular Multilevel Converter (FB-MMC) containsmany switching devices and is low in utilization ratio of the switchingdevices and high in operation loss. With this regard, the patentWO2012103936A1 proposes a Half Bridge and Full Bridge sub-module basedhybrid Modular Multilevel Converter (HBFB-MMC) solution, which has theadvantages of both HB-MMC and FB-MMC and reduces about ¼ of switchingdevices compared with the FB-MMC solution while having the DC faultclearance capability, and thus the solution has broad applicationprospects.

In the HBFB-MMC solution, as shown in FIG. 1, the sub-module basedhybrid converter includes at least one phase unit; each phase unitincludes an upper bridge arm and a lower bridge arm; the upper bridgearm and the lower bridge arm each include at least one half bridgesub-module, at least one full bridge sub-module, and at least oneresistor which are connected in series; and an AC side of the converteris connected to an AC power grid by means of a charging resistor as wellas a bypass switch and an incoming switch thereof. The half bridgesub-module includes at least two turn-off devices with antiparalleldiodes and an energy storage element. A negative pole of the firstturn-off device is connected to a positive pole of the second turn-offdevice to form a first bridge; a positive pole of the first turn-offdevice serves as a positive pole of the first bridge; a negative pole ofthe second turn-off device serves as a negative pole of the firstbridge; a connecting point between the first turn-off device and thesecond turn-off device serves as a first terminal of the half bridgesub-module; the negative pole of the first bridge serves as a secondterminal of the half bridge sub-module; the positive pole of the firstbridge is connected to a positive pole of the energy storage element,and the negative pole of the first bridge is connected to a negativepole of the energy storage element. The full bridge sub-module includesat least four turn-off devices with antiparallel diodes and an energystorage element. A negative pole of the first turn-off device isconnected to a positive pole of the second turn-off device to form afirst bridge; a positive pole of the first turn-off device serves as apositive pole of the first bridge; a negative pole of the secondturn-off device serves as a negative pole of the first bridge; and aconnecting point between the first turn-off device and the secondturn-off device serves as a first terminal of the half bridgesub-module. A negative pole of the third turn-off device is connected toa positive pole of the fourth turn-off device to form a second bridge; apositive pole of the third turn-off device serves as a positive pole ofthe second bridge; a negative pole of the fourth turn-off device servesas a negative pole of the second bridge; a connecting point between thethird turn-off device and the fourth turn-off device serves as a secondterminal of the full bridge sub-module; the positive pole of the firstbridge and the positive pole of the second bridge are connected to thepositive pole of the energy storage element, and the negative pole ofthe first bridge and the negative pole of the second bridge areconnected to the negative pole of the energy storage element.

During the uncontrolled charging, all half bridge sub-modules areblocked, and all full bridge sub-modules are blocked. FIG. 5 illustratesa schematic diagram of the uncontrolled charging of the half bridgesub-module. When the current flows in the first terminal, the energystorage element of the half bridge sub-module is connected in series tothe charging circuit, and the energy storage element is charged. Whenthe current flows out of the first terminal, the energy storage elementof the half bridge sub-module is not connected in series to the chargingcircuit, and the energy storage element is not charged. FIG. 6illustrates a schematic diagram of the uncontrolled charging of the fullbridge sub-module. When the current flows in the first terminal, theenergy storage element of the full bridge sub-module is connected inseries to the charging circuit, and the energy storage element ischarged. When the current flows out of the first terminal, the energystorage element of the full bridge sub-module is also connected inseries to the charging circuit, and the energy storage element ischarged. Since the charging duration of the full bridge sub-module isabout twice that of the half bridge sub-module, the voltage of the fullbridge sub-module is about twice that of the half bridge sub-moduleduring uncontrolled charging. Moreover, in the high-voltage situation,the operations of sub-modules depend on the self-powered supply. Ingeneral, the starting voltage of the self-powered supply cannot be low.In this case, the half bridge sub-module is not controlled in the ACuncontrolled charging stage, and the next full-controlled chargingprocess cannot be carried out. Therefore, it is necessary to design acharging method for a sub-module based hybrid converter to raise thevoltages of the half bridge sub-modules in the uncontrolled stage of thehalf bridge sub-modules, thereby increasing the starting point of thesub-module based self-powered supply and reducing the design difficultyof the sub-module based self-powered supply.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a charging methodfor a sub-module based hybrid converter according to the characteristicsof AC uncontrolled charging of a Half Bridge and Full Bridge sub-modulebased hybrid Modular Multilevel Converter (HBFB-MMC), so as to implementthe smooth charging of the HBFB-MMC without reducing the startingvoltage of the sub-module based self-powered supply and complete thestarting process.

To achieve the above objective, the present invention adopts thefollowing technical solutions:

A charging method for a sub-module based hybrid converter, where themethod includes the following specific charging steps:

step (1): performing, by a converter, an uncontrolled charging process;

step (2): powering a full bridge sub-module based self-powered supply,and half-blocking full bridge sub-modules according to voltages in adescending order after the powering succeeds, the full bridgesub-modules being half-blocked one by one or multiple at a time, andduring the process, the remaining full bridge sub-modules that are notbypassed being blocked, and all half bridge sub-modules being maintainedin a blocked state; and

step (3): performing, by the converter, a full-controlled chargingprocess after all the full bridge sub-modules are half-blocked.

As a further preferred solution of the present invention, each halfbridge sub-module includes at least two turn-off devices withantiparallel diodes and an energy storage element; a negative pole ofthe first turn-off device is connected to a positive pole of the secondturn-off device to form a first bridge; a positive pole of the firstturn-off device serves as a positive pole of the first bridge; anegative pole of the second turn-off device serves as a negative pole ofthe first bridge; a connecting point between the first turn-off deviceand the second turn-off device serves as a first terminal of the halfbridge sub-module; the negative pole of the first bridge serves as asecond terminal of the half bridge sub-module; the positive pole of thefirst bridge is connected to a positive pole of the energy storageelement, and the negative pole of the first bridge is connected to anegative pole of the energy storage element.

The full bridge sub-module includes at least four turn-off devices withantiparallel diodes and an energy storage element; a negative pole ofthe first turn-off device is connected to a positive pole of the secondturn-off device to form a first bridge; a positive pole of the firstturn-off device serves as a positive pole of the first bridge; anegative pole of the second turn-off device serves as a negative pole ofthe first bridge; a connecting point between the first turn-off deviceand the second turn-off device serves as a first terminal of the halfbridge sub-module; a negative pole of the third turn-off device isconnected to a positive pole of the fourth turn-off device to form asecond bridge; a positive pole of the third turn-off device serves as apositive pole of the second bridge; a negative pole of the fourthturn-off device serves as a negative pole of the second bridge; aconnecting point between the third turn-off device and the fourthturn-off device serves as a second terminal of the full bridgesub-module; the positive pole of the first bridge and the positive poleof the second bridge are connected to a positive pole of the energystorage element, and the negative pole of the first bridge and thenegative pole of the second bridge are connected to the negative pole ofthe energy storage element.

As a further preferred solution of the present invention, thehalf-blocking the full bridge sub-module in step (2) specifically is:turning on the first turn-off device of the full bridge sub-module,turning off the second, third and fourth turn-off devices or turning offthe first, second and third turn-off devices, and turning on the fourthturn-off device.

As a further preferred solution of the present invention, thefull-controlled charging process in step (3) refers to blocking some ofthe half bridge sub-modules, and bypassing some of the half bridgesub-modules; and half-blocking some of the full bridge sub-modules, andbypassing some of the full bridge sub-modules.

As a further preferred solution of the present invention, the bypassingthe half bridge sub-module refers to turning off the first turn-offdevice of the half bridge sub-module and turning on the second turn-offdevice.

As a further preferred solution of the present invention, the bypassingthe full bridge sub-module specifically is: turning off the first andthird turn-off devices of the full bridge sub-module, turning on thesecond and fourth turn-off devices or turning on the first and thirdturn-off devices, and turning off the second and fourth turn-offdevices.

The present invention also discloses a charging method for a sub-modulebased hybrid converter, where the method includes the following specificcharging steps:

step 1: performing, by a converter, an uncontrolled charging process;

step 2: powering a full bridge sub-module based self-powered supply, andbypassing full bridge sub-modules according to voltages in a descendingorder after the powering succeeds, the full bridge sub-modules beinghalf-blocked one by one or multiple at a time, and during the process,the remaining full bridge sub-modules that are not bypassed beingblocked, and all half bridge sub-modules being maintained in a blockedstate;

step 3: half-blocking all the full bridge sub-modules and blocking allthe half bridge sub-modules after the average voltage of the half bridgesub-modules is K times greater than the average voltage of the fullbridge sub-modules, where 0.6<K<1.4; and

step 4: performing, by the converter, a full-controlled chargingprocess.

As a further preferred solution of the present invention, thefull-controlled charging process in step 4 specifically is: blockingsome of the half bridge sub-modules, and bypassing some of the halfbridge sub-modules; and half-blocking some of the full bridgesub-modules, and bypassing some of the full bridge sub-modules.

As a further preferred solution of the present invention, each halfbridge sub-module includes at least two turn-off devices withantiparallel diodes and an energy storage element; a negative pole ofthe first turn-off device is connected to a positive pole of the secondturn-off device to form a first bridge; a positive pole of the firstturn-off device serves as a positive pole of the first bridge; anegative pole of the second turn-off device serves as a negative pole ofthe first bridge; a connecting point between the first turn-off deviceand the second turn-off device serves as a first terminal of the halfbridge sub-module; the negative pole of the first bridge serves as asecond terminal of the half bridge sub-module; the positive pole of thefirst bridge is connected to a positive pole of the energy storageelement, and the negative pole of the first bridge is connected to anegative pole of the energy storage element.

The full bridge sub-module includes at least four turn-off devices withantiparallel diodes and an energy storage element; a negative pole ofthe first turn-off device is connected to a positive pole of the secondturn-off device to form a first bridge; a positive pole of the firstturn-off device serves as a positive pole of the first bridge; anegative pole of the second turn-off device serves as a negative pole ofthe first bridge; a connecting point between the first turn-off deviceand the second turn-off device serves as a first terminal of the halfbridge sub-module; a negative pole of the third turn-off device isconnected to a positive pole of the fourth turn-off device to form asecond bridge; a positive pole of the third turn-off device serves as apositive pole of the second bridge; a negative pole of the fourthturn-off device serves as a negative pole of the second bridge; aconnecting point between the third turn-off device and the fourthturn-off device serves as a second terminal of the full bridgesub-module; the positive pole of the first bridge and the positive poleof the second bridge are connected to a positive pole of the energystorage element, and the negative pole of the first bridge and thenegative pole of the second bridge are connected to the negative pole ofthe energy storage element.

As a further preferred solution of the present invention, thehalf-blocking the full bridge sub-module specifically is: turning on thefirst turn-off device of the full bridge sub-module, turning off thesecond, third and fourth turn-off devices or turning off the first,second and third turn-off devices, and turning on the fourth turn-offdevice.

As a further preferred solution of the present invention, the bypassingthe half bridge sub-module specifically is: turning off the firstturn-off device of the half bridge sub-module and turning on the secondturn-off device.

As a further preferred solution of the present invention, the bypassingthe full bridge sub-module specifically is: turning off the first andthird turn-off devices of the full bridge sub-module, turning on thesecond and fourth turn-off devices or turning on the first and thirdturn-off devices, and turning off the second and fourth turn-offdevices.

By using the above solutions, the present invention has the followingbeneficial effects:

(1) the charging method provided by the present invention can raise thevoltages of the half bridge sub-modules in the uncontrolled stage of thehalf bridge sub-modules;

(2) the charging method provided by the present invention can increasethe starting point of the sub-module based self-powered supply, reducethe design difficulty of the sub-module based self-powered supply,achieve the smooth charging of the HBFB-MMC without reducing thestarting voltage of the sub-module based self-powered supply, andcomplete the starting process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a half bridge and full bridge sub-module based hybridmodular multilevel converter;

FIG. 2 is a single line diagram of a HVDC converter station;

FIG. 3 is a first flowchart of charging;

FIG. 4 is a second flowchart of charging;

FIG. 5 is a schematic diagram of blocking a half bridge sub-module;

FIG. 6 is a schematic diagram of blocking a full bridge sub-module;

FIG. 7 is a schematic diagram of half-blocking a full bridge sub-module;

FIG. 8 is a schematic diagram of bypassing a half bridge sub-module; and

FIG. 9 is a schematic diagram of bypassing a full bridge sub-module.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions of the present invention are described belowwith reference to the accompanying drawings and the specificembodiments.

The sub-module based hybrid converter mentioned in the followingembodiments is shown in FIG. 1, where a first turn-off device Q1 h and asecond turn-off device Q2 h of a half bridge sub-module, as well as afirst turn-off device Q1 f, a second turn-off device Q2 f, a thirdturn-off device Q3 f, and a fourth turn-off device Q4 f of a full bridgesub-module are shown.

A charging method for a sub-module based hybrid converter, where an ACside of the converter is connected to an AC power grid by means of acharging resistor as well as a bypass switch and an incoming switchthereof, as shown in FIG. 2; the charging steps are shown in FIG. 3, andthe specific steps are as follows:

(1) closing the incoming switch QF so that the charging resistor of aconverter valve performs an uncontrolled charging process, closing thebypass switch QA after the charging current is less than a set valueIset or the DC voltage is greater than a set value Uset, and bypassingthe charging resistor, where Iset<0.1 pu and Uset>0, and in this case,the voltage of a full bridge sub-module is about twice that of a halfbridge sub-module, and the voltages of the both are low;

(2) selecting N full bridge sub-modules with the highest voltage tohalf-block after a full bridge sub-module based self-powered supply issuccessfully powered, where N increases from 0 gradually, the remainingfull bridge sub-modules are blocked, all half bridge sub-modules areblocked, as N increases gradually, the average voltage of the halfbridge sub-modules increases gradually, the average of the full bridgesub-modules also increases gradually, and the two voltages approachgradually, so that the voltages of all the full bridge sub-modules areequalized; and

(3) performing a full-controlled charging process after all the fullbridge sub-modules are half-blocked and when the average voltage of thehalf bridge sub-modules approaches the average voltage of the fullbridge sub-modules.

The half-blocking the full bridge sub-module refers to turning off Q1 f,Q2 f, Q3 f, turning on Q4 f or turning off Q2 f, Q3 f, Q4 f, and turningon Qlf, as shown in FIG. 7.

The bypassing the half bridge sub-module refers to turning off Q1 h andturning on Q2 h, as shown in FIG. 8. The bypassing the full bridgesub-module refers to turning off Q1 f and Q3 f, turning on Q2 f and Q4 for turning off Q2 f and Q4 f, and turning on Q1 f and Q3 f, as shown inFIG. 9.

In the full-controlled charging process, the voltage equalization of thetwo types of sub-modules is taken as a control target. If the halfbridge sub-modules and the full bridge sub-modules are sorted in aconcentrated manner, these sub-modules operate according to the voltageequalization strategy and gating method provided in the existingliterature; if the half bridge sub-modules and the full bridgesub-modules are sorted in groups, then these modules are distributedaccording to the total bypass number of each bridge arm, and thenoperate according to the voltage equalization strategy and gating methodprovided in the existing literature.

A charging method for a sub-module based hybrid converter, where an ACside of the converter is connected to an AC power grid by means of acharging resistor as well as a bypass switch and an incoming switchthereof, as shown in FIG. 2; the charging steps are shown in FIG. 4, andthe specific steps are as follows:

(1) closing the incoming switch QF so that the charging resistor of aconverter valve performs an uncontrolled charging process, closing thebypass switch QA after the charging current is less than a set valueIset or the DC voltage is greater than a set value Uset, and bypassingthe charging resistor, where Iset<0.1 pu and Uset>0, and in this case,the voltage of a full bridge sub-module is about twice that of a halfbridge sub-module, and the voltages of the both are low;

(2) selecting N full bridge sub-modules with the highest voltage tobypass after a full bridge sub-module based self-powered supply issuccessfully powered, where N increases from 0 gradually, the remainingfull bridge sub-modules are blocked, all half bridge sub-modules areblocked, and as N increases gradually, the average voltage of the halfbridge sub-modules increases gradually, and the voltages of all the fullbridge sub-modules are equalized;

(3) half-blocking all the full bridge sub-modules and blocking all thehalf bridge sub-modules after the average voltage of the half bridgesub-modules is K times greater than the average voltage of the fullbridge sub-modules, where 0.6<K<1.4; and

(4) performing a full-controlled charging process.

The half-blocking the full bridge sub-module refers to turning off Q1 f,Q2 f, Q3 f, turning on Q4 f or turning off Q2 f, Q3 f, Q4 f, and turningon Q1 f, as shown in FIG. 7.

The bypassing the half bridge sub-module refers to turning off Q1 h andturning on Q2 h, as shown in FIG. 8. The bypassing the full bridgesub-module refers to turning off Q1 f and Q3 f, turning on Q2 f and Q4 for turning off Q2 f and Q4 f, and turning on Q1 f and Q3 f, as shown inFIG. 9.

In the full-controlled charging process, the voltage equalization of thetwo types of sub-modules is taken as a control target. If the halfbridge sub-modules and the full bridge sub-modules are sorted in aconcentrated manner, these sub-modules operate according to the voltageequalization strategy and gating method provided in the existingliterature; if the half bridge sub-modules and the full bridgesub-modules are sorted in groups, then these modules are distributedaccording to the total bypass number of each bridge arm, and thenoperate according to the voltage equalization strategy and gating methodprovided in the existing literature.

The foregoing embodiments are used to explain the technical idea of thepresent invention, but are not intended to limit the scope of protectionof the preset invention. Any modification made based on the technicalsolutions according to the technical idea of the present invention shallfall within the scope of protection of the present invention.

The invention claimed is:
 1. A charging method for a hybrid converterbased on half bridge sub-modules and full bridge sub-modules, whereinthe method comprises the steps: step (1): performing, by a converter, acharging process; step (2): powering a self-powered supply of the fullbridge sub-modules and half-blocking the full bridge sub-modules,half-blocking the full bridge sub-modules comprising the steps of:turning on a first turn-off device of the full bridge sub-modules,turning off a second, third and fourth turn-off devices or turning offthe first, second and third turn-off devices, and turning on the fourthturn-off device, then based on a sequence from high to low of a voltageof each of the full bridge sub-modules, starting with a full bridgesub-module having a greatest voltage of the full bridge sub-modules, andcontinuing with other full bridge sub-modules, after a poweringsucceeds, the full bridge sub-modules being half-blocked one by one ormultiple at a time, and during the process, other full bridgesub-modules that are not bypassed being blocked, and all half bridgesub-modules being maintained in a blocked state; and step (3):performing, by the converter, a full-controlled charging process afterall the full bridge sub-modules are half-blocked.
 2. The charging methodfor the hybrid converter based on half bridge sub-modules and fullbridge sub-modules of claim 1, wherein each of the half bridgesub-modules comprises at least two turn-off devices with antiparalleldiodes and an energy storage element; a negative pole of the firstturn-off device is connected to a positive pole of the second turn-offdevice to form a first bridge; a positive pole of the first turn-offdevice serves as a positive pole of the first bridge; a negative pole ofthe second turn-off device serves as a negative pole of the firstbridge; a connecting point between the first turn-off device and thesecond turn-off device serves as a first terminal of the half bridgesub-modules; the negative pole of the first bridge serves as a secondterminal of the half bridge sub-modules; the positive pole of the firstbridge is connected to a positive pole of the energy storage element,and the negative pole of the first bridge is connected to a negativepole of the energy storage element; each of the full bridge sub-modulescomprises at least four turn-off devices with antiparallel diodes and anenergy storage element; a negative pole of the first turn-off device isconnected to a positive pole of the second turn-off device to form afirst bridge; a positive pole of the first turn-off device serves as apositive pole of the first bridge; a negative pole of the secondturn-off device serves as a negative pole of the first bridge; aconnecting point between the first turn-off device and the secondturn-off device serves as a first terminal of the half bridgesub-modules; a negative pole of the third turn-off device is connectedto a positive pole of the fourth turn-off device to form a secondbridge; a positive pole of the third turn-off device serves as apositive pole of the second bridge; a negative pole of the fourthturn-off device serves as a negative pole of the second bridge; aconnecting point between the third turn-off device and the fourthturn-off device serves as a second terminal of the full bridgesub-modules; the positive pole of the first bridge and the positive poleof the second bridge are connected to a positive pole of the energystorage element, and the negative pole of the first bridge and thenegative pole of the second bridge are connected to the negative pole ofthe energy storage element.
 3. The charging method for the hybridconverter based on half bridge sub-modules and full bridge sub-modulesof claim 1, wherein the full-controlled charging process in step (3)refers to blocking some of the half bridge sub-modules, and bypassingsome of the half bridge sub-modules; and half-blocking some of the fullbridge sub-modules, and bypassing some of the full bridge sub-modules.4. The charging method for the hybrid converter based on half bridgesub-modules and full bridge sub-modules of claim 2, wherein thebypassing the half bridge sub-modules refers to turning off the firstturn-off device of the half bridge sub-modules and turning on the secondturn-off device.
 5. The charging method for the hybrid converter basedon half bridge sub-modules and full bridge sub-modules of claim 2,wherein bypassing the full bridge sub-modules is performed by: turningoff the first and third turn-off devices of the full bridge sub-modules,turning on the second and fourth turn-off devices or turning on thefirst and third turn-off devices, and turning off the second and fourthturn-off devices.
 6. A charging method for a hybrid converter based onhalf bridge sub-modules and full bridge sub-modules, wherein the methodcomprises the steps: step 1: performing, by a converter, a chargingprocess; step 2: powering a self-powered supply of the full bridgesub-modules, and bypassing the full bridge sub-modules starting with afull-bridge sub-module having a greatest voltage of the full-bridgesub-modules, based on a sequence from high to low of a voltage of eachof the full bridge sub-modules and continuing with other full-bridgesub-modules after a powering succeeds, the full bridge sub-modules beinghalf-blocked one by one or multiple at a time, and during the process,other full bridge sub-modules that are not bypassed being blocked, andall half bridge sub-modules being maintained in a blocked state; andstep 3: half-blocking all the full bridge sub-modules and blocking allthe half bridge sub-modules after an average voltage of the half bridgesub-modules is K times greater than an average voltage of the fullbridge sub-modules, wherein 0.6<K <1.4; and step 4: performing, by theconverter, a full-controlled charging process.
 7. The charging methodfor the hybrid converter based on half bridge sub-modules and fullbridge sub-modules of claim 6, wherein the full-controlled chargingprocess in step 4 specifically is performed by: blocking some of thehalf bridge sub-modules, and bypassing some of the half bridgesub-modules; and half-blocking some of the full bridge sub-modules, andbypassing some of the full bridge sub-modules.
 8. The charging methodfor the hybrid converter based on half bridge sub-modules and fullbridge sub-modules of claim 6, wherein each of the half bridgesub-modules comprises at least two turn-off devices with antiparalleldiodes and an energy storage element; a negative pole of the firstturn-off device is connected to a positive pole of the second turn-offdevice to form a first bridge; a positive pole of the first turn-offdevice serves as a positive pole of the first bridge; a negative pole ofthe second turn-off device serves as a negative pole of the firstbridge; a connecting point between the first turn-off device and thesecond turn-off device serves as a first terminal of the half bridgesub-modules; the negative pole of the first bridge serves as a secondterminal of the half bridge sub-modules; the positive pole of the firstbridge is connected to a positive pole of the energy storage element,and the negative pole of the first bridge is connected to a negativepole of the energy storage element.
 9. The charging method for thehybrid converter based on half bridge sub-modules and full bridgesub-modules of claim 8, wherein half-blocking the full bridgesub-modules is performed by: turning on the first turn-off device of thefull bridge sub-modules, turning off the second, third and fourthturn-off devices or turning off the first, second and third turn-offdevices, and turning on the fourth turn-off device.
 10. The chargingmethod for the hybrid converter based on half bridge sub-modules andfull bridge sub-modules of claim 7, wherein bypassing the half bridgesub-modules is performed by: turning off the first turn-off device ofthe half bridge sub-modules and turning on the second turn-off device.11. The charging method for the hybrid converter based on half bridgesub-modules and full bridge sub-modules of claim 8, wherein bypassingthe full bridge sub-modules is performed by: turning off the first andthird turn-off devices of the full bridge sub-modules, turning on thesecond and fourth turn-off devices or turning on the first and thirdturn-off devices, and turning off the second and fourth turn-offdevices.